A Moderately Thermophilic Mixed Microbial Culture for Bioleaching of Chalcopyrite Concentrate at High Pulp Density

Abstract

ABSTRACTThree kinds of samples (acid mine drainage, coal mine wastewater, and thermal spring) derived from different sites were collected in China. Thereafter, these samples were combined and then inoculated into a basal salts solution in which different substrates (ferrous sulfate, elemental sulfur, and chalcopyrite) served as energy sources. After that, the mixed cultures growing on different substrates were pooled equally, resulting in a final mixed culture. After being adapted to gradually increasing pulp densities of chalcopyrite concentrate by serial subculturing for more than 2 years, the final culture was able to efficiently leach the chalcopyrite at a pulp density of 20% (wt/vol). At that pulp density, the culture extracted 60.4% of copper from the chalcopyrite in 25 days. The bacterial and archaeal diversities during adaptation were analyzed by denaturing gradient gel electrophoresis and constructing clone libraries of the 16S rRNA gene. The results show that the culture consisted mainly of four species, includingLeptospirillum ferriphilum,Acidithiobacillus caldus,Sulfobacillus acidophilus, andFerroplasma thermophilum, before adapting to a pulp density of 4%. However,L. ferriphilumcould not be detected when the pulp density was greater than 4%. Real-time quantitative PCR was employed to monitor the microbial dynamics during bioleaching at a pulp density of 20%. The results show thatA. calduswas the predominant species in the initial stage, whileS. acidophilusrather thanA. caldusbecame the predominant species in the middle stage.F. thermophilumaccounted for the greatest proportion in the final stage.